Pretty true. To kinda expound on that, it works "up," but it can get stuck on local maxima rather than global maxima. Picture two mountains separated by a valley and one being higher than the other. If a species is 'climbing' the smaller peak of fitness then once it gets there it can theoretically never climb down the valley and start climbing the taller mountain. It will always* be stuck on that smaller peak because Evolution doesn't know how to take short term pain for long term gain. It's effectively a greedy algorithm to borrow from a CS concept.

*As long as conditions stay exactly the same. The adaptive landscape is always changing.

Not always. There's a great example of an evolutionary study on a bird species that had incredibly long tails. Like, tails that were so long that they often interfered with flight and made the bird significantly more likely to be caught by predators.

However, the females preferred males with longer tails. So, what essentially happened is that the male birds continued to grow their tails as long as they possibly could until they hit a sort of critical threshold of being maximally attractive for females, but juuuust short enough that it didn't completely hinder their ability to get away from predators and fly.

Researches assayed this by taking feathers and artificially elongating certain male bird's tails (basically bird hair extensions). They noted that these doctored birds had significantly higher mating rates than other birds, but on the flip side, they also got caught (and killed) by predators much more often.

There's tons of examples of this throughout nature, where sexual selection essentially overrides the fitness loss for 'deleterious' traits.

Evolution is honestly a lot more nuanced than people generally realize. Even deleterious mutations and traits can rise to fixation in a population despite our understanding of fitness models.

Adding to this, no evolutionary biologists look at traits in organisms today and explain how / why they evolved by how they are beneficial. To do so is teleogical, explanation by the purpose they serve rather than the process by which they came to be. It also ignores that sometimes traits serve no actual purpose. They can arise to fixation randomly or the trait is vestigial for some other functions that are no longer relevant, but now serve a different purpose. A good example is that, in the case of human hairlessness, the reason why is still actually a pretty hotly debated subject because we don't really know.

Generally speaking, in order to confirm a trait's purpose and evolution you have to study the impact on fitness when you remove that trait and you have to use nearest relatives or most common ancestors to show how the trait evolved in the model species in question.