Object got unstuck from printing mat So I was trying to print 3DBenchy on my new Wanhao i3+. PLA plastic, basic high quality settings in Cura (I guess 0.06 mm layer, 40 mm/s speed, 50c bed temp, 195c extruder temp). I didn't use any tape, just regular wanhao printer mat, which was installed on printer bed from the box.

At some moment when I looked I found things fouled up: object came off from the mat and sticked to the extruder and was moving with it. 
It printed like 3-4 mm of the object (about 50 layers) before this happened.

I would like to know what are the main reasons this can happen? And what can I do to prevent this? I think it's very sad when you lose many hour of work.
You have to secure your print to the build plate.  

One thing that I always do is to use a brim in cura.  prints a single layer which extends in all direction away from your object, adding extra adhesion between your object and the print bed.

You can also use a slower extrusion speed for your initial layer but I would use this after trouble shooting everything else since you will be adding time to each print.

If you are using a heated bed make sure that the temperature is set for the correct material.  For PLA i think that is 40C-60C.

We put down a layer of craft/school elmers stick glue before most prints.  This helps a bit with adhering to the build plate, and also seems to allow the prints to pop off a bit easier. 

Also be sure to double check you Z calibration and your bed level.  If there are inconsistencies and your nozzel moves to far away from you bed, you will be extruding in air and not getting and stickage at all.