Some things make total sense to validate outwardly:
If you’re working on a project for a client, then it makes sense that the client should be the one to validate whether or not your work meets expectations.
If you’re trying to sell a product, then it makes sense to let the market validate its commercial viability — after all, it’s of little use if only you think your product is good.
On the other hand, certain things — namely, your happiness — make way more sense to validate inwardly.
Predicating happiness on the validation of others invariably sets you up for a roller coaster ride that, in most cases, isn’t terribly enjoyable.
On the other hand, your sense of contentment is most stable when you validate your happiness inwardly — when you choose to be happy irrespective of the opinions and actions of others.
This doesn’t mean you ignore the outside world or resolve to feel nothing in light of events that, by most accounts, would be deemed unfortunate.
The trick — the punchline — is recognizing that you can choose how to respond.