explain plan and the real execution plan

Hi, all:

I have a question about the explain plan. 


Under what conditions, could the plan I get out of 'explain plan' differ
from what I get from running the sql statement?


Suppose the database has no change during I ran 'explain plan' and run
the sql - I mean, no ddl and dml - You would think this database is
static. Or the time gap between I run 'explain plan' and run sql
statement is too narrow to allow any change (ideal environment). No bind
variable peeking because _optim_peek_user_binds is set to FALSE.


Any idea? Thanks in advance.



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