This tool is quite helpful for calculating the odds of various dice rolls for comparison of how traits can be used to change the odds under different dice mechanics.

Dice Pool

In this approach the number of dice you roll is equal to your trait value (some skills might start with one die). These are all rolled to achieve at least one die with a given value. We'll call these changes to succeed "easy," "normal," and "hard." In addition you could change the probabilities by requiring more than one success roll out of the pool...this starts to get complicated. But it’s undoubtedly fun to roll a fistful of dice.

2d6 Target Number

In this approach you roll 2d6 and add the trait, trying to reach a target number. There is not a lot of wiggle room in the spread of numbers, so negative and positive adjustments are significant.

Increasing difficulty is the same as removing trait points, and vice versa, so there is flexibility with this system: you can determine a higher challenge level is lower for a skilled player, or you can keep the challenge level and let the player add their trait score to their roll. It may sometimes be a little of both.

Aligning to the dice pool mechanic above, you would choose 8+ for easy, 9+ for normal, and 11+ for hard, but notice that this is much more difficult than the targets as described below. Unlike the dice pool case, with a target number approach, you have two more options for targets (above easy).

Names for these challenge levels: