For example, Bogle's "buy everything and hold it forever" only works when you're not really doing that, and you're buying an index. But any market cap weighted

For example, Bogle's "buy everything and hold it forever" only works when you're not really doing that, and you're buying an index. But any market cap weighted index is doing EXACTLY not that. It by definition has to reduce and increase weighting of constituents over time because their valuations change over time... including going to ZERO.