The noun pinnacle is used to talk about the highest or culminating point of something, most commonly the time in one’s career when they are most successful or a specific achievement that caps one's career. In architecture, a pinnacle is a small, upright structure rising above the roof of a building or capping a tower. In nature, a pinnacle is a lofty peak of a mountain or a pointed, towering part of a rock formation. The theme of capping, crowning, or being positioned atop something is what threads these senses together. The more general word peak is the appropriate choice for talking about maximum prices (oil prices reached their peak) or maximum volume (traffic was at its peak).
To fret over something is to feel or express worry, annoyance, or annoyance about it. The earliest senses of this term in English had to do with devouring or consuming in the literal sense—as in moths fretting your favorite sweater (heaven forbid!). The verb has of course evolved since then, with the theme of consuming taking a turn: rather than expressing the act of consuming, fret now conveys being consumed or eaten by something. Interestingly, the critters who would do the fretting were usually small (like moths), which perhaps explains why the current sense of fret suggests incremental or gradual gnawing away at one’s peace of mind.