Second Answer
You are 2nd seat, unfavorable. Say that you open one spade, West doubles, partner passes, and East bids two clubs.
Are you strong enough to bid game, strong enough to invite game, or not strong enough to invite game?. Partner probably won’t have much in high cards but might well have the sort of “little something” that you need for game. Here is one way to think about it: if partner has one or more spades, you should want to be in game even if partner has nothing else useful. You’re at least two-to-one to take seven spade tricks and it’s certain you will take at least three heart tricks. So, although you may be too high if partner is void in spades, we think you need to bid four spades here.