This is what your characters aspire to be; not what they are right now.
This is what is holding them back from answering the question “can I achieve my ideal?”
This is a broad-strokes, single phrase description of the type of person your character has been in the past.
Can my character act out of alignment? Yes.
What is the consequence of this? Internal conflict and angst. How you deal with that internal conflict might have consequences in game mechanics (for example, losing paladin features). Other consequences include social treatment. If you have been neutral good in the past and suddenly you are acting evil then the people who know you will be surprised, puzzled, and perhaps hurt. They will certainly treat you differently.
Can my character change their personality? Yes. I’ll be disappointed if they don’t. Characters change (hopefully for the better). Flaws, ideals, bonds, even alignment can change. Not often, however. Perhaps once every power tier?
Part of the story that we are creating at the table is “does my character achieve their ideal or not?” If all goes well, we will answer this question at the climax of the game’s action.
Note that the answer does not have to be “yes” — failure is just as interesting as success.
I believe that the GM’s job is to challenge the colour of the character’s spirit, just as much as it is to challenge their skills and abilities.
If you rise to this challenge, you will be rewarded.