Victor Wooten wrote a book about engaging and learning music called The Music Lesson. His first message - one I very strongly agree with - is that The Groove Comes First. More than scales, chords, and other technique or theory. It is the access point to the music.
The bass is typically the melodic instrument whose job is to establish and hold the groove. A good bass player understands that is Job 1.
Is Little Green Bag the quote you were looking to dig up? 
I’m trying to remember what does the bassist lock into with the drummer? Is it the kick drum beat? High hat? I’ve never really understood what the various parts of the drum set are for.
Anyway, when the bass and drummer are in the groove magic happens. Fights can break out when the bassist and drummer aren’t on the same page. 
Usually the drummer is carrying the beat on one or two drums, and doing accents/fills with the rest of the kit. You try to lock with those. But what drum they’re carrying the beat with changes depending on the song/style. Usually it’s the snare, the high hat, ride or the bass drum, but if you’re doing say, a Bo Diddley beat, it’s probably going to be on the floor toms.
Even though I’ve never felt any compelling reason to try to lock with say…the wind chimes, there’s probably an appropriate song out there for doing that.
At the risk of sounding lecture-y, per my post above, the best answer is really “the groove established by/with the drummer.”
In jazz, it is often the high hat. With rock, it is usually kick and snare on a backbeat groove. With disco it was four-on-the-floor kick. Whatever establishes the groove.
Oh good gawd - you dredged up distant memories of trying to play rock with a jazz drummer, imploring him to get off that damned high hat! 
Thank heavens for bluegrass, where all I have to do is intimidate the occasional mando picker! 
Not to turn this into a bluegrass discussion, but in BG bass is really boiled down to it’s basics. The main thing is to drive the beat, and remain SOLID. As a low-talent roleplayer - I LOVE it! Sure you can add in runs, and some slapping, but if you just focus on playing every note as solid as possible, you will never lack for gigs.
Now rockabilly is an entirely different beast. Sure, the quitarists still get the glory, but whatever their pyrotechnics, they are NOTHING compared to an accomplished slapper!
I need to start listening closer to the drummer and listen for the count. Usually I listen for the bass. Bass always signals chord changes and sets the beat.
Bass and percussion are often expected to serve as rhythm section, while the vocals and guitar do more complex stuff. Many bands have a singer who also plays bass, because bass riffs aren’t important nor complex enough to focus more attention on.
If you’re not giving the bassist cool stuff to do, he doesn’t get to look cool.
That said, cool bassists exist. Jaco Pastorius was all right. Even Sting wrote some good bass lines.
Quite the understatement, there.
A historical tidbit to illustrate a point: the Beatles kept the hopeless Stu Sutcliffe on bass for a long time. Why? Because SOMEBODY had to play it, and nobody else wanted to. EVERYBODY wanted to play guitar, Paul most definitely included.
When Paul reluctantly agreed to play bass, he bought a Hofer from a pawn shop, mainly because it was cheap, and his frugal Dad had always told Paul not to go into debt (by contrast, John and George had bought expensive guitars on credit).
It’s all about that bass, is what you’re saying.
Nothing like Queen’s John Deacon to show how the bass player can be great and still be, for the casual observer/listener, outshone.
Lead Vocals and Piano: Freddie motherfuckin’ Mercury. Already your chances of showing off are down by 90%.
Guitar and Vocals: Brian May. Simply, a guitar god with an instantly-recognizable sound.
Drums and vocal: Roger Taylor. Superb drummer and harmony vocals into the stratosphere.
Then there’s
Bass and ocasional live vocals: John Deacon
The other three guys have all the flair, show and everything. But still, Deacon’s basslines did more than hold things together, they were interwoven with the songs in a way that no quarter-eighth-eighth bass player can.
Also, lower frequencies don’t sound that well on lower-quality equipment.
As many said, it IS easier to play.
I love the “offensive lineman” comparison. Few kids grow up wanting to be an Right Guard and they are not that well known, but when you know your American/Candian football, you know how important they are if it is not a “skill position”.
Ají de Gallina, laying tight basslines at children’s Mass for 7 years.
Before they got to their current ages, Geezer Butler was a good example, whereas the most Tony Iommi would do (in terms of stage presence) is stroll around while blasting out his riffs.
Mike Inez is another good example btw.
Composing, and to a lesser extent performing bass lines at the level of John Deacon takes tremendous talent and skill, and is in no way “easier” than creating and performing the guitar or drum parts.
I was refering to bass (in general) being easier than guitar or keyboards.
Deacon’s line are not easy at all
I had a kinda difficult jam session today. Yesterday I spent over an hour just working the metronome. Man, I was solid. Then this morning, it was all out the window. The mandos and fiddles especially kept rushing things. Sure, they were playing a lot more notes, but none of them had to be as concerned as me about keeping everyone together.
Playing the notes is easy. Playing each note perfectly, less so. Driving a solid beat while various showboats speed up and slow down - not easy at all. Fortunately, most of the show boats appreciate what the bass brings.
I’m not any sort of musician, and would not have attempted to answer the main question, but compared to the OP’s friend, I was able to name quite a few famous bassists by process of elimination.
Well, that is your value! Everyone else is playing the embellishments to the song, you’re holding the song down. You’ve got to communicate to them (yes, while pretty much playing the roots), that they’re rushing. Though, I think working to a metronome is almost counterproductive. It’s more about the feel that erupts from the whole than working to a particular BPM.
Yep, that’s the only glory of the job. When the drummer (ok, not in your case) and everybody else is rushing, you’ve got to drag the beat enough to slow them down. Sometimes they listen, sometimes everyone else in the band thinks you are wrong. So it goes.
When I started playing rhythm guitar, I was like superRhythm Guy! Why do one strum when a dozen flourishes will do!
As I realized how important it was to stay coordinated with a group, I simpled down beyond belief. Strum Strum Strum Strum - big, obvious beats, with minimal stuff between them. Also, started making eye contact with each person - if we didn’t have our hands full making music, I would be looking for them to swipe the side of their nose “are we good?/are you in on this groove we are making?”
My bass player is the first guy I make eye contact with. I am looking for his beat, not expecting him to hit mine. He signs off on my groove, then I go hound everyone else and make sure we are ready for changes. The bass player is staying locked in with the drummer and selling his backing vocals. Meat and potatoes gig work - the groove comes first!
It must be very different for a nonplayer to not have this perspective. The bass is in the center of the conversation and a lead player is on the fringe, benefitting if the center holds. The question is how hard the core parts of the band are trying to listen to each other.
Trying to anchor jams can be pretty challenging. I feel that if I’m going to maintain that I am holding THE beat, I need to be sure of myself that I AM as solid as I think. So - yeah - I practice A LOT with a metronome. Ususally more slow than fast, just trying to make each note as solid as possible. Playing ahead/behind, or right on it. Of course, I realize that playing live is different, but if I don’t know where the beat is, then I don’t have a good idea of how I’m deviating from it and why.
Generally I’ll lock in with a mando. But just about 100% of the time, they’ll ramp it way up when they take a break. Fiddles too. And you generally don’t want to just keep ramping it up and up every break. And since my MAIN role is keeping things steady, I always tend to take it personally when things go south.
The WORST are those people who simply have NO sense of timing. The speed up, slow down, add and drop beats indiscriminately. You really wonder how someone can be as oblivious as that. :rolleyes: