The main cause for this problem is that the address is wrong. Certain games store an extra screen value for each and every value. For example, there can be one value for health and another one for displayed health. So, the changes that you make for one value has no impact on the thing that you have searched for. Also, certain changes you make on certain games might not display until you make the next move. For example, the number of ammo you changed might not be visible until you start firing.