Filter out the pseudo-elements!
05AB1E, 9 8 bytes

-1 bytes thanks to Magic Octopus Urn

ηOO¹g/‹Ï


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η        # Get prefixes
 O       # Sum each
  O¹g/   # Get the mean ( length(prefix list) equals length(original list) )
      ‹Ï # Keep only the value that are less than the mean




05AB1E, 6 bytes

Using the new ÅA command.

ηOÅA‹Ï


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η      # Get prefixes
 O     # Sum each
  ÅA   # Get the mean
    ‹Ï #  Keep only the value that are less than the mean