It's a good rule of thumb that you should generally move all-in or fold with 10bb or less (no ante) and 15bb or less (with an ante). The reason is that the starting pot is so large compared to your stack that it's vital to maximize the chance that everybody folds. Also, any small raise comes close to committing you to the pot anyway!
You're completely, however, that these guidelines aren't absolute. Here are a few exceptions:
** You open-limp a weak hand in the small blind against a very weak-passive opponent with 10bb.
** With an ante, you min-raise K3o on the button for 14bb against passive blinds.
** With an 8bb stack, you min-raise AA in late position in a freeroll against maniacs left to act.
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