He is working his servants hard.

The earliest use of latent variable ideas in time series appears to have been due to Wiggins (1973) but, as so often happens, it was not followed up. […] The basis for this remark can be explained by reference to a simple example which, at first sight, appears to have little to do with latent variables.

a lofty goal

Don't be afraid to kick it around a little. It is sturdy.