How can a theory be reliable or consistent over time if personality is believed to change?

Because theories are based on facts, evidence and observation not on personality, if something happens or is discovered to alter those facts, evidence or observations then the theory is either amended, altered or accepted as wrong, again personality has nothing to do with it. Gravity is a theory, evolution is a theory, E=Mc2 is a theory... they are not facts but as yet nothing as been discovered to disprove what they suggest and all experimentation so far has supported what they propose hence they are accepted as the "facts". If anyone can come up with an alternative that better explains what they do then they will immediately be disregarded and the new theory will become the accepted on. Again, personality has nothing to do with it.