There are tons of similar questions, but I still do not understand the essence of the problem. I have SBT project where custom appender is defined. Fully qualified class name is specified in logback.xml file. Play project explicitly dependsOn that project with appender. When Play is started the classpath includes the path to the class of appender, but I see the error. On the other side the same appender is instantiated without any error for Akka project. So what is so special for loading a class having the absolute path to the directory where class files sit?

ClassNotFoundException when instantiating custom logback appender in Play

There are tons of similar questions, but I still do not understand the essence of the problem.

I have SBT project where custom appender is defined.
Fully qualified class name is specified in logback.xml file.
Play project explicitly dependsOn that project with appender.
When Play is started the classpath includes the path to the class of appender, but I see the error.

On the other side the same appender is instantiated without any error for Akka project.

So what is so special for loading a class having the absolute path to the directory where class files sit?