So, you bought a house for $1m and a year later someone offers you $900k for it. Will you sell it? Why should you? If you're not in debt, have money to pay your bills, you won't sell it, right?
another scenario is buying this house for a million then someone offering $1.2 million
yes you have made profit but is $200k really the best profit you can make? just because the price has already gone up means you should immediately jump the ship and sell it especially that there is a big chance that the price is still gonna rise up if you could just wait for a little bit
be patient and do not be impulsive do not get too excited and always look at the bigger picture