can you please edit this post to take your nipple off the page... it disturbs me just to kind of clarify... as a general rule.. every set of reps you do the last rep you should should struggle to perform whether you're looking for:

Power/strength - 1-4 reps (usually performed anaerobically)
Strength/bulk (depending on diet) - 6-8 reps
Muscular endruance - 10+ reps...

Each last rep you should fail on.... and just to again clarify, fail does not mean drop the weight as your body cannot take anymore, it's just when you lose form...