For mine, it was when he realized that being a PO was his best shot at playing past high school. Honestly, I think the answer comes a little easier to lefties than to righties, just because the field positions are more limited for the vast majority of lefties. Some of the key factors leading to his understanding:
*He is a lefty
*He is not fast. Most college recruiters, especially at the higher levels, recruit up the middle of the field. The faster you are, the better your shot.
*He can hit for some power, but he is not a consistent masher. Takes him out of the college level hitting debate, especially with his slower speed.
That doesn't mean he can't still play a position for his high school. At the high school level, he can hit well (has been a designated hitter since sophomore year) and he can make up for his slightly slower speed in the outfield by getting good reads on the ball.
For this summer (as a rising senior), he was offered a PO spot on one of the best club teams in our area. He decided it was a good offer. It has been a positive learning experience. Now he has a more realistic understanding of what college baseball will be like for him.
We do know a couple of 2017 grads who will be playing at the D1 level as two-way players, so it's not unheard of. But, you need to really have something special to play both ways. BTW, both kids are lefty pitchers/outfielders who can hit the snot out of the ball on a consistent basis against very high level pitching.
For some reason, this has been a really hot topic around here the last few weeks. There are quite a number of threads with a lot of really good info that you can search for.