The ultimate cause of the problem is the amount and quality of the electricity flowing through the body.
1) The path of flow: Smaller currents can cause fatalities if the internal organs are located in the path for current flow.
If the shock is applied between the arms, as in holding Neutral and Live wire in one hand, it can cause death. If the shock delivery points are one arm and one leg, the same source of electricity might not prove fatal.
This is likely also why electrocution can be executed by placing electrodes across the head. This ensures that the current runs through the brain.
2) Resistance of your body: This refers to the resistance that the body offers to electric flow. It can vary depending upon the moisture level. As mentioned above, it can also change with voltage.
3) Voltage. It is important to remember that the body’s resistance changes with voltage. It is not a linear increase in voltage with current (according to ohm’s law).
Skin is an insulator and greatly contributes to high resistance (order Mega-ohms for low voltages). High voltages can cause dielectric breakdown, which reduces the resistance by nearly 1000 times.
It is this that makes voltages higher than a certain point fatal. Current flow can increase dramatically.
4) The duration of shock: In general, the longer the shock lasts, the greater the damage.
Static electricity is an interesting example. Static electricity can easily be created at levels exceeding 10000 Volts. This is enough to cause air to fall short distances. Handshakes don’t cause any deaths. 🙂
This is because while static has a lot of potential, its total source charge is very small. The current flow’s duration is too short to have any effect.
To answer your question, although it is the electron flow (current) that causes problems, other factors (including voltage), can have a significant impact on how much electron flow occurs.