PROBLEM #8 – Backstabbed wires are more likely to come loose
8. BACKSTABBED WIRES
What it means: On newer switches and receptacles, wires pushed in the back are more likely to come loose than those anchored around screw terminals.
Code violation? No. The practice is allowed, even for new construction.
Danger level: It depends. At a minimum, loose wires can cause a receptacle or switch to stop working. In the worst case, they can start a fire.
Solution: Check for back-stabbed connections by removing a switch or receptacle from its outlet box. If one is back-stabbed, there are likely to be more. Release the wires and attach them to the appropriate screw terminals on the receptacle.
Information that is being provide is for Educational Purpose, Any electric work that is needing to be done, should be done by a Licensed Electrician.
Source:This Old House