I have long enjoyed chart-based resolution systems, such as those in Rolemaster, Mythic and others. While they may feel cumbersome at first, they provide a few advantages:
They reduce the amount of rules needed to remember, and they provide a wide range of possible outcomes, that would take complex mechanics or math to get otherwise.
OSR games are unique in that they tend not to have a resolution mechanic at all. Rather than having a universal system for resolving actions, each situation is often taken on it's own merits. Even then, many groups adopt their own unique ways of handling things, which is part of what makes the OSR so interesting.
The Action&Event table presented here is essentially a universal resolution mechanic. The player states what they are trying to achieve, you roll percentile dice and read the result. The results can and often will require significant interpretation, which can lead your game in entirely unexpected directions.
It is assumed that the action is reasonably achievable, and so the table does not factor in difficulty. If an action is particularly easy, don't bother getting out the dice for it. If something is insanely hard, the player should try to take steps to better his odd's, until the DM agrees that he qualifies for an Action&Event roll.
The DM should have an idea of possible consequences of a failed action.
It's worth noting that there are too many results on the table to make it easy to memorize. This is rather intentional.
1-2 Character suffers a permanent flaw
3-5 Complete disaster - Action fails in the worst possible way
6-9 Character fails completely at the task.
10-14 Action fails and the character suffers a consequence of failure
15-19 Action fails but character avoids consequences
20-24 Action fails due to an unforeseen circumstance
25-29 Failure to make progress. Character needs to change approach or make situation easier to retry
30-34 Failure to make progress. If time isn't a concern, can attempt it again
35-39 Unexpected event interrupts action
40-50 Action barely succeeds
51-65 Action succeeds with a consequence
66-90 Action succeeds as expected
91-95 Action succeeds, character makes unexpected discovery
96-98 Action succeeds perfectly
99-100 Character develops a new talent
Only one modification is made: If the character is judged to be good at the action, a result of "Failure to make progress" permits a second attempt to be made immediately, but the second roll stands.