One thing players, especially new players often hear is that they shouldn't worry about skills because a skill at level 4 is usually only 5% less effective then level 5. In fact, often the difference is much less. It sounds good, but it is not really true. What people often forget is that skills multiply. A 5% rate of fire decrease, and a 5% damage bonus, gives a 10% bonus. Having multiple skills at level 5 vs another player with level 4 skills, adds up quickly to be overwhelming. Lets look at a Rifter as an example.
Below is the quintessential rifter fit with all level 5 skills.
Here is the same fit with all level 4* skills:
* Note: Having all skills at level 4 is actually impossible since some skills (like small projectile specialization) require other skills to be at level 5.
As you can see there is a huge difference. A 19% drop is DPS is nothing to ignore. But that is not all. Since skills such as fall-off, range and tracking are also impacted if you look at the DPS graph with one ship going at full speed, the difference is even more extreme.
Here you can see at even the best range for the level 4 skilled ship, the DPS is dropped by fully 22%. Hardly the 5% difference that is often claimed. The level 5 player will not even be in structure when the level 4 player is popped.
While it is very true that skills are not a simple 'I Win' button; tactics, positioning, picking fights, understanding mechanics and all that do matter more; they do matter a lot. Don't discount them.