Talk at wroclove.rb 2019 by Dimitry Salahutdinov. Argues that spinners upset users and that UIs should optimistically assume success, citing the 98% figure for successful AJAX requests and Google's RAIL performance model (>100ms delay loses user focus). Reviews challenges of optimistic UI — network errors, offline mode, server errors, merge conflicts — and introduces Logux, a framework invented by Andrey Sitnik that treats client and server as a distributed system communicating over WebSockets, with event sourcing, CRDT-like last-write-wins merging, time-shift ordering via timestamp+counter, and undo events for server-side error handling. Demonstrates the logux-rails Ruby gem integrating with Rails via a Logux proxy, showing Amplifr demos of project rename, post discussion chat, and centralized currency-rate updates pushed from the backend. Mentions Anton Davydov's next-day event-sourcing talk for a deeper dive.