Yes exactly single strategy may not always work and if one knows how to use such strategies and when to use will easily get profit out of it. We hear about strategies from longer time and i may not seen that some of these strategy fails to work but the main thing which matters is that a person should have knowledge about the proper time to use it.

It does not refer to the fact that for success new strategies will arise but it means that you will use the old strategies but in different time for different coins. No one can disregard the old strategies because these all are in use and no one can disregard the benefit of using these strategies.