Tell me reality of electron flow in any complex circuit

Just one. Electrons flow from the negative point to the positive point in any available path.

By convention ‘current’ flows from the positive to the negative. If there is no difference in voltage between any two points, there is no flow.

Try imagining an electrical wire as a big pipe with marbles. Those marbles are electronics and they go from negative to positive. As those marbles flow - they create 'voids' that are filled up with imaginary 'positive' charge - which obviously appears to flow from positive to negative. 

Does this help?