Where do you find motivation?

The Key to motivation in any task is focusing on the rewards, be they long or short-term.

If you worked knowing you weren't going to be paid- you'd do it really awfully. But if you were promised a big paycheck for a job or a promotion- you're gonna work like never before.

So bascially just focus on what you'll be achieving once the task is completed.

The best way to find motivation is to recall the last time when you were pretty much motivated and "memorizing" this state by anchoring it. This will let you ALWAYS be motivated.

Look up the Motivation Anchoring Technique.

Depends on what the task is - i.e. for motivation there is a need and a reward - i.e. where you are now is unsatisfactory, and you believe you can take action to improve your situation. There's then other factors - self-esteem, support of others, intermediate rewards, distractions, attention (and impulisivity - both correlated to working memory), forward planning, feasability of achievement, etc.

in yourself.

You just need to be determined in order to be motivated.