1. Bitcoin is Highly Volatile: you need to understand that Bitcoin is highly volatile in nature meaning it is not constant in it's price the price changes every minute meaning it rises and falls frequently so If you use money meant for your rent, food, or bills, you risk being stranded during a fall of Bitcoin price.
Using only your Discretionary income protects your lifestyle even if Bitcoin falls.
Price changes in split second and not even up to a minute, Bitcoin is highly volatile and the only way to catch a specific price is by starting buy it sell orders. When you but outside your discretionary funds, there is a total of selling in loss of Bitcoin is experiencing a negative price correction below your every point at the time you wish to use the invested funds. Furthermore, it's best practice tho but with discretionary income so you can go for a long-term holding plan with your investment.