Reason: You will need money in future that you can't foresee now.
Like Medical, or future purchasing opportunities when market crashes or something. It doesn't necessarily means something bad will happen. Something great might also happen like a land or house going for cheap or even other assets(things that make money).

Should be clear enough from the title. And if you think I am asking you to be selfish, I am not.

I WANT you to lend money to friends and people in need.
I want you to do that but I only want you to do that if you are already good enough financially.

It might sound pretty easy and common sense but when a close friend asks for money, remember that it's a bad precedent to set.

In flight it's being taught all the times to mothers in case of low oxygen first take oxygen yourself & then give the baby oxygen.
But many over-protective mothers die along with the baby because they give the baby the oxygen first and the baby can't give your oxygen back so you die and the oxygen cup falls from your hands and babies die.

You are basically doing the same thing when you lend money to someone when you're yourself not well off financially.

Make better choices in life so that you have a lot of money and money that keeps growing that lending money to others doesn't affect your finances.

As a wise man said,

साँई इतना दीजिए, जामे कुटुम समाय।
मैं भी भूखा ना रहूँ, साधु न भूखा जाय।।

Nobody knows what will happen in future. I am not saying the person you're lending the money is bad or greedy but life happens.
He/She might seriously need an extension on the time or might even not be in a situation to pay it back.
You might even feel worse even asking for money.

Literally never do that. Alright. NEVER INVEST WITH DEBT. End of story.