Secrets of professional chess
We all play chess for different reasons.
For some of us chess is an exciting game for leisure time or mind exercise. Once chess becomes a sport for you, the approach to the game changes drastically. It is not enough just to love the game (but that too). You must play even if you don't feel like that. You must play to win. There is no excuse. You need to practice regularly, memorise positions, read, learn, train your "mind muscles". It is a never-ending search for ideas and improvements. The same regular physical sports rule applies: if you do not exercise - you get weaker. Being a sportsman requires to eliminate the factor of bad-luck-dependent result. All possible bad factors should be eliminated or minimised. Noise resistance, emotional stability, concentration - all of those should be in norm. Stamina is one of the tools that serves the purpose of the above qualities. Mikhail Botvinnik (known for his tournament and match preparation) had his own system of body and spirit training. The health component in chess is as important as our ability to count variations. A lot of the professional chess players were into physical sports too, e.g. Spassky played tennis, Petrosian was into football etc. Physical sport makes you more durable, adapted to a long period of intensive brain work.
I noticed for myself that having not enough sleep deteriorates my mood to play chess. Most of chess players do IT-related jobs for living. Having excessive computer work makes you want to close your eyes and rest not even thinking about chess. Playing after an intense day at work is very hard.
Once you have a flu, even slight thinking gives you headache. I strongly recommend adjourn the game and not to play when you are sick. Quitting a tournament is also an option as the health is more important and playing sick will not make any good.
Many people laugh at the fact that chess is considered a kind of a sport. Indeed, you won't get a hernia from lifting chess pieces. Neither you can get a fracture or injury unless falling off your chair. However, achieving a sport result in chess is even harder that in a regular sport. Chess is an intensive battle of minds that requires racking your brain for good 4-5 hours. I can compare that only to a marathon run. And as in every sport - the fittest wins.