I think the reason is important. If you stick to something because you think it is the right thing to do, that is conviction. If you stick to something because you think you must continue as you have already invested effort into, that is sunk cost. The point that I'm trying to make, that perhaps I have not worded well, is that you must act with conviction, because if you do not do what you think is right, you either not do anything, or do what you think is wrong. Sure, you may be wrong at the time, and you should be open to reflection, and not be prey to sunk cost.
But coming up with convenient excuses to avoid doing what you think is inconvenient but right is not how leaders behave.
And in this context (if that is what you mean), it is definitely not evident that supporting Ukraine is a strategy that won't work.