Developers know there’s always time pressure, either from management, or the client, to deliver results. And in often unrealistic timescales.
Even with the best briefs you need to fully understand all the design parameters to meet expectations and deliver results. And you need time to unpick the brief, think outside of the box, anticipate roadblocks and other potential issues. Development is not linear, it takes time, skill, trial, error, repeat, until the successful coding or technical solution is achieved.