I've sold tons of Bitcoin at around $200 and also sold even more ETH at around $5-$10 a coin. I sold because at the time it looked like a fair price and I needed to money to pay for electricity and buy more GPUs.
Yes if I've held till now I would definately get much more for it but you can't predict the future. At the time BTC when it traded around $200 it looked like it would break $200 support and head into the $100 area and maybe even double digits. And ETH at the time of the DAO hack was not looking good either, and it could of went back to $1 ETH a coin.
Sure if I knew what the future would bring I've obviously would of held but I didn't. Same with you selling at $3000. You said you knew it was going to go up but how sure were you? Not very. It could of went to $2000 then $1000 and you wouldn't be able to buy food like you've meantioned.
I sold close to 30 BTC in 2015, when the prices were around $200 per coin. I was without a job for 6 months in 2014, and was facing some financial crunch. I would say that the proceedings from that sale saved me from complete meltdown. But it can be hard not to think about what could have happened, had I held onto those coins. I could have received 100x, for a total of $600,000 instead of $6,000. That amount is not large enough to make me retire from the full time job, but I could have purchased my dream home. I still have some coins and my current target price is $250,000 per coin. I am not going to make this foolishness of selling most of coins ever again. The current prices ($10,000 per coin) doesn't look attractive enough, and if it is needed then I am ready to wait for another three-four years.