Sometimes the measure of a good programmer is knowing what exists in the language, but also knows what exists in the ecosystem around the language and deciding what to use. Because sometimes community created functionality (libraries, API's and methods) can end up being better than the native ones.

Take Javascript for example, plenty of native methods for manipulating collections (arrays, maps and so on) but then you have Lodash (a Javascript toolbelt) with its own implementations of native methods which in many cases outperform the native version, such as iterating collections and search through an array of objects by object key.

The biggest improvement any developer can make is learning to read the documentation, read it before you do anything. Far too many times I see people get into trouble and the answers are right there in the documentation, but they don't read it.