Here's a nice piece of witticism  from the Psycho-Cybernetics classic by Dr Maxwell Maltz for you to ponder:

"... I failed once in the past, so I will probably fail in the future" is neither logical nor rational.

To conclude "I can't" in advance, without trying, and in the absence of any evidence to support the inevitability of failure, is not rational.

We should be more like the man who was asked if he could play the piano.

"I don't know," he said.

"What do you mean you don't know?" he was, asked.

"I have never tried," he replied... "

On a contemporary note, just think about what billionaire entrepreneur Elon Musk once said:

"If something's important enough, you should try. Even if - the probable outcome is failure. 

I'd rather be optimistic and wrong than pessimistic and right. If you get up in the morning and think the future is going to be better, it is a bright day."