What goes into a concrete mixer is water, sand, cement and aggregate – very different raw materials that can do a very good job on their own right but which have limitations to their use and application (sounds a bit like Trust members).
What comes out of a concrete mixer is concrete – an extremely durable, versatile, flexible and long standing product that has many different and varied applications. It’s highly adaptable and, depending on the mix of raw materials, can be used for a broad range of jobs and applications.
The thing about a concrete mixer though is that once you’ve poured the raw ingredients in, you’ve got a small amount of time to get the job of mixing done and the concrete poured out of the mixer before it sets. Therefore it requires a high degree of skill to balance a highly volatile set of materials, that can go off at any time once they are mixed together, without ruining the end product (sounds a bit like the Trust).