The mobile space is still very young, relatively speaking, and it evolves at an incredible pace. With Apple and Google heavily investing in their platforms, the speed with which mobile platforms evolve requires developers to focus and learn non-stop.
In 2015, Apple introduced no less than two new platforms, tvOS and watchOS. While developers familiar with iOS won't have a hard time getting up to speed with Apple's brand new SDKs, there are many, many APIs and paradigms to become familiar with. It is understandable if you feel a little overwhelmed as a mobile developer.
If you decide to become a developer, regardless of the platform you write software for, you need to accept and become comfortable with the fact that learning on a daily basis is part of the job.
For the past few years, Apple has released a new version of its operating systems every year, introducing new technologies every developer needs to become familiar with. The Swift project continues to evolve at a fast pace. Swift 3 was released last month and with it came new features, numerous bug fixes and improvements, and several paradigm shifts.
Are you ready to dive in head first? If Apple announces a slew of new APIs next year, will that scare you or will it excite you? Do you have the motivation to not only continue learning but also push the envelope. Using an API is one thing, pushing it to its boundaries and beyond is where it's at.
If you like programming, but prefer to stick with what you know, then mobile development may not be the best choice. If learning is in your blood and the mere thought of WWDC or Google I/O gives you goosebumps, then being a mobile developer is the best job in the world.