Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Why will the bank only loan us 80% of the value of our fully paid for home?
Imagine the bank loaning 100% of the sum of money you needed to buy a house, if the valuation of the house decreases to 90% of the original price after 3 months, would it be unfair for them to ask them for 10% of the original price from you immediately? I suppose the rationale for loaning 80% is so that you will fork our 20% first, and so your property is protected from fluctuations in the market, that they do not need to collect additional money from you as your housing valuation rarely drops below 80% of the original price. Banks do need to make money too, as they run as a business.