The one that got away

Sometimes fishing can give you the best highs you can think of. Like when you catch a really big fish in an unexpected situation or moment. You're pumped, the body is shaking and full of adrenaline.

But it can also be very hard and unfair. Most of us will endure this at least once in the fishing career and we can't prevent this from happening.
Imagine the following:

You're fishing a very hard water where not every day is catch day.
You grind your fly on all good places where you know the fish are holding or feeding, but nothing worked for the last few weeks.
Out of the sudden you get the bite you are waiting for so long. There is a heavy opponent on the other site of the line and you directly feel this is the one fish, you are after for a long time.
But then the line gets slack and you can't really realize what has happen.
Depraved you strip the line in and check the leader. Everything is okay, the fly is still in tact and the hook is sharp as a razor blade.

Every time this happen to me, I want to scream, throw my rod into the water and roll down on the bottom like an embryo. I know that's how fishing can be, but for that moment I'm just frustrated.
One thing I learned is to keep going and do the next cast. You have to get the negative thoughts out of your brain and focus on fishing again. I realized when I think too much about a lost fish, I can't focus on the further fishing and might fuck up another good bite.
Be positive, focus on the fishing and have confidence in your doing. Then the next bite of the big one will come and you are able to land it.