Happened to me a year ago when I used outdated version of core wallet and it had fee hardcoded (?) and it was lower then needed. Transaction never got confirmed, newegg order got cancelled, BTC returned back to the account after a while.
Which is why we must familiarize ourselves with our wallets before doing anything else, or we may end up doing silly mistakes, that almost happened to me once when I was about to send a transaction and then I noticed that my wallet was not in mBTC but in BTC so I was about to send a transaction 1000 times larger than what was needed, so I saved myself a lot of money and trouble by double and triple checking the details of the transaction.