Designing Encounters RPG Class 101

I am in to my third decade of DMing and I thought I would share my ideas on Encounter creation.
Golden rule dont make all the encounters the same level of difficulty!! What seems to work best for me is to create a mix of easy,medium, hard and a few impossible encounters.
The easy encounters are used to help build the confidence of the players. You really dont want too many of these as they can become boring.
The medium encounter present some danger and a little better payoff, but still shouldn't result in the death of anyone. The majoritry of encounter should be this type.
The hard encounters are the one that people remember the most. They are the fun ones, the one where death is a real possibily. The payoff are good. This is where the party finds the magic sword they have been questing for. You should have at least one of these in a session.
And lastly the impossible (or nearly impossible) encounters. These encounters are designed to bring the players back to reality (in a fantasy kind of way) These encounters (if the party doesn't run) would result in the death of everyone. On the other hand if the party is very creative and does manage to overcome the encounter then this is the stuff of legend! This is where the mega payoff is, wishes, holy advengers etc..This type of encounter should rarely be used as it can be discouraging if overused.
I have found that this mix of encounter difficulties works very well.

Cheers!