In the minutes leading up to me performing a maximal lift, I picture myself performing that lift. I get nervous and I get butterflies. However as I approach the bar something changes and I believe I can do it. All doubt leaves my mind and I feel a determination I can’t really explain.
It hasn't always been like this. I have failed lifts before because in my mind I wasn't fully convinced I could do it. Like with anything I think becoming good at performing maximal lifts comes with practice. This doesn't mean you should try maxing out every time you go to the gym. As well as this not being very clever from a training point of view, I think it sets you up for long term failure.
A few years back when my ultimate squat goal was 200kg I was testing myself far too often to see if I could achieve it. Each time I didn't the element of failure would be on my mind even just before I performed the rep. As I've had more experience in lifting heavy weights in different environments my skill of performing when it matters has improved. This is in addition to smarter training methods and following better programmes.
The other thing testing at the right times has allowed me to do, is have a better understanding of how heavy I should go when deciding what weight to lift. Looking back a few years I was probably picking loads that I didn't have any chance of lifting anyway. Add in the factors mentioned above and it’s little surprise I had hit a plateau for so long. Nowadays when I’m going for maximal lifts more often than not I lift what I set out to do.
Testing your lifts more infrequently, allowing yourself to make more progress before testing again in my opinion is the way to go about things. It allows you to practice your skill of lifting heavy as well as allowing you to hopefully hit a new personal best each time.