The D&D alignment system is a good tool but characters can and do change over time, in fact that movement from one alignment to another can be a good way to make a character interesting and how susceptible to such movement a character is can be an important trait to consider when creating them.
For example, Janna is quite susceptible to alignment change and has been chaotic neutral, chaotic good, lawful neutral and lawful good depending on how events in her life have affected her but Severn is quite rigid and has consistently been lawful good.
It takes a lot more than alignment to create a rounded character, though.
