Oracle's Mutating Trigger Error Explained through Analogy
A mutating trigger error in Oracle SQL can be compared to trying to taste cake batter while it's still being mixed or asking how many books are on a shelf while it's being rearranged. This is because the table (cake batter or bookshelf) is being updated, and the trigger (taste the cake or count the books) is trying to read or modify that table while it's mid-update. Oracle blocks this action to prevent errors. To fix this issue, complete the update first, then process data later using statement-level triggers or temporary storage.

Source: https://dev.to/mrcaption49/analogy-of-mutating-trigger-with-examples-3n1o