After the incident which caused Leonard's condition in Memento, he cannot remember anything more than a few minutes old, other than the events before that incident. Yet, he remembers his condition?
Leonard cannot remember his condition. Sometimes he even forgets what he is doing at the moment. Remember the scenes when he is running because he is being chased or when he drinks the beer with spit in it. He just suddenly loses any clue why is he doing something. After the accident, he said he cannot store recent memories, but he can remember everything before the accident. He has to be reminded of the incident (he does it by viewing his tattoos, notebook, etc). His tattoos reminds him of everything - about the condition. Look carefully:
He remembered Sammy Jankis, who had a special condition.
He remembers the accidents.
By remembering Sammy Jenkins, he remembers he has a similar condition.
He now confirms his weakness.
He reminds himself how he can try to remember things.
This is the way he reminds himself about his condition and the other facts he is looking for. Sam Jankis is a fictional character through which he remembers he has the condition. Sammy is a character from Leonard's memory where the memory of Leonard and Sammy is mixed.
All the tattoos listed by Mistu4u help Leonard in guiding himself to cope with his conditions.
However even in this condition he never forgets daily chores like driving, eating, shaving etc. He is also able to use English language comfortably. Through his subconscious he knows about his condition too.
he doesn't remember his condition but every time that he forgets things and he feels like he has just woken up, he first looks around (so he sees his left hand at the very first moment) and the tatoo