Some of the many mistakes I have made are that of being " lazy" and instead of creating some tables and some schema structure and all the related code I just serialized the stuff and stored it as a string in the database. A few month later or less a very simple be requirement arise and I have to filter by a thing inside the serialization string. Then I say ok, let's index separately the thing, or store it independently, or do two pass filtering, but none of these beats the very simple query I could have done if I had done the right thing in the first place. I hid the complexity away but it came back to me weeks later and then it really stunk: the choice is between many evils, migrate existing data, duplicate the thing, select by regexp, etc.
impression (Noun) 1. An idea, feeling, or opinion about something or someone, esp. one formed without conscious thought or on the basis of little evidence.