Question about General rel and quanta phys

[HappySkeptic]

There are 3 things that are odd about quantum mechanics

1. Entanglement - often called "spooky action at a distance"
   
2. Uncertainty - the more precisely we know where something is, the less precisely we know its momentum, and vice-versa
   
3. Measurement - all properties are probabilities (described by the wavefunction) until measured.  But what is measurement?  In the Copenhagen Interpretation, it is the collapse of the wavefunction, but how, why, and when does that happen?  It is not clear how a universe of probabilities becomes a fixed reality on macroscopic scales, and yet it does.
   

All 3 of these things are important when talking about small ensembles of basic particles.  They become less important when we get more massive objects.