GM TipIt is important to know when and when not to invoke the skill system. There are certain actions or situations which would not logically require the use of a skill. For example, most characters can tie their own shoes, or even drive a car, under normal circumstances. Anyone, even someone with no skill at knife fighting, can slit the throat of an unconscious opponent with no difficulty.
Skills should only be used when there is a measurable chance of failure. Trying to control the aforementioned car while hurtling down a twisting mountain road after the brakes fail is obviously much more difficult, and would require the use of a skill. Somewhere between the extremes lies the line at which the skill must be used. Where exactly that line lies is often a judgment call, completely left up to the GM.
In cases of indecision, where the line is not obvious, or when the character should have a better chance of success than indicated by their skill level, it is common practice to allow some sort of positive modifier (or negative difficulty) to the skill check.
Obviously, it would be possible to take this to the extreme, and start levying +90 modifiers to things the character really should be able to accomplish easily. This can lead to frustration when players manage to fail these rolls (and it will happen). It can also slow things down. ("I get up and have breakfast." "Okay. Make a willpower check at +85 to get yourself out of bed, an agility check at +80 to walk downstairs without falling, and a cooking check at +90 to make toast.") This gets tedious really fast.