A library declares what it needs, an application declares what it uses, and a resolver picks a version that satisfies both. When it cannot, the error names the two ranges that do not overlap, and reading that is the whole skill of a broken install.
About 1 min of reading
Find the conflict.
Two ranges
Before you run it, say out loud what it will print. Then open the answer.
Read the first example one line at a time. A line that prints shows what appears on screen; the rest set things up quietly.
A command that prints the chosen version for every dependency is the state of an install. Publishing that output with a release is what makes the release reproducible.
Install with the lowest allowed version of each dependency. A test that only passes at newest is a test that hides a range that is too wide.
The resolver says A needs >=1.4 and B needs <1.4. Those two ranges do not overlap, so no version exists. The fix is changing one of the declarations, not trying a new number.
A range that allows any major is a range that will accept a breaking change. Narrowing to the majors you tested is what makes an upgrade a decision rather than an accident.
Two parts of a system needing different majors of the same library cannot both be satisfied in one process. That is a design problem, and the resolver error is the only place it is visible.
Each one is defined here on this site. Open the entry for the full definition and the other words it points at.