I happened upon the service record of President McKinley, which is an interesting read, and was inspired to raise a difficult hypothetical. (This has most likely been done before here.)
You joined the army near the outset of the (whichever) war, finding yourself in the ranks of the infantry. Over the course of 30 months, you consistently impressed your superiors with your abilities and have risen to an upper rank of Major.
Now you have been tasked, along with Major Kestrel (who is of a slightly lower grade than you) with delivering two large battalions (about 2000 troops) to Villaford in anticipation of a significant battle.
Along the way, one of your scouts comes back with a report of an enemy column traversing the valley of the Breakneck, about half a mile away over the ridge, toward Villaford. There are probably 20,000 men in the column.
Major Kestrel looks at the map, sees a convenient bend farther down the valley, and outlines a plan whereby your contingent could ambush the column, from both the front and rear, and probably wipe them out or drive them back up the valley (Kestrel is a much keener strategist than you).
If you undertake this enterprise, which will likely cost a significant fraction of your men, and succeed, the shortage of enemy at Villaford will almost certainly turn that battle in favor of your side, even if you show up there late or short-handed. Villaford is very important, and a decisive victory there would likely spell an end to the war in weeks.
Your chance of success is about two in three, because you know Major Kestrel is a fine strategist and you and your team of officers are excellent co-ordinators. Your orders were to bring these battalions to Villaford, but there was no literal injunction against skirmishing along the way. Nonetheless, doing this, even successfully, would almost certainly earn you a reprimand and perhaps a medal.
The war has given you a path of advancement. If it is over in less than a month, that ends for you, especially in light of a reprimand. If you proceed to Villaford, given the size of the enemy column, your side will not win this battle (even with receiving intelligence about the column), and the war will probably go on well into the next year, giving you more opportunity to rise in rank.
What do you do?