A characteristic of a conservative force is that an object returning to its starting point will return with no loss of kinetic energy because if the initial and final points are the same. If a ball is tossed into the air, energy is transformed from kinetic into potential and back such that the ball’s kinetic energy is unchanged when it returns to its initial height. The same is true for a puck sliding up and back down a frictionless slope.
But not all forces are conservative forces. If the slope has friction, then the puck returns with less kinetic energy. Part of its kinetic energy is transformed into gravitational potential energy as it slides up, but part is transformed into some other form of energy—thermal energy—that lacks the “potential” to be transformed back into kinetic energy. A force for which we cannot define a potential energy is called a nonconservative force. Friction and drag, which transform mechanical energy into thermal energy, are nonconservative forces, so there is no “friction potential energy.”
Similarly, forces like tension and thrust are nonconservative. If you pull an object with a rope, the work done by tension is proportional to the distance traveled. More work is done along a longer path between two points than along a shorter path, so tension fails the “Work is independent of the path followed” test and does not have a potential energy.
All in all, most forces are not conservative forces. Gravitational forces, linear restoring forces, and, later, electric forces turn out to be fairly special because they are among the few forces for which we can define a potential energy. Fortunately, these are some of the most important forces in nature, so the energy principle is powerful and useful despite there being only a small number of conservative forces.