Hit Confirmable Strings
Learning what strings can be hit confirmed (both normal hit and counter hit) is essential to making sure you aren't on the losing side of a battle.
The first thing you should notice is that all the CH confirmable strings will KND and/or launch on hit, whereas the Non-CH confirmable strings will leave the opponent standing on hit.
Hit Confirmation vs Anticipation:
There should be a clear distinction between hit confirming and "confirming" via anticipation, as I'm fairly sure that many newer players don't truly hit confirm their strings. For instance, your opponent's back is to the wall and frames are on your side so you opt to use 1,2,1. You see the opponent flinch and assume that they're attacking, so you finish the string assuming that they'll be wall splatted. This is obviously the case of "anticipation," because you were making assumptions, assumptions that the opponent would attack and you'd beat them out 100% of the time. A flinch is very hard to distinguish from a counter hit but the ability to realize if they were attacking or not comes with experience.