I have weird stuff happening

. I want to make a small trainer and all.. all that part is ok for me. It is just that in some game, it seem that i find the adresse of a value (life for example) but when i change it to the max (at 999 or anything else with cheat engine for example) it is like i did not do any change and the life keep decreasing as it was but when it change, i can still see the value decreasing but when i change it, it is like i din't do anything.... weeiird i say!.
I dont need a full tutorial or a detailed explanation about how to do this and that. I can manage to do that myself. The best way to learn is by searching ourself but sometime, i need a hint about where to go or where is my mistake.
Thank again all for any usefull support.