Mars in Sagittarius makes its first, major aspect: a delusional square to Neptune Rx at 5 degrees Pisces (from September 17 to 21).
Neptune weakens Mars. It dissolves initiative, or misdirects it. Mars in Sag is barreling ahead at full speed, but as it encounters the square to Neptune, its momentum will slow and diffuse. Neptune/Pisces and Sagittarius involve expansion, but with the square, that expansion will be over idealized or false.
This aspect illustrates the phrase "tilting at windmills;" charging ahead on an illusionary crusade. Or, galloping towards your escape, which will end up being a confusing detour.
Fortunately, this aspect is brief. You'll feel it if you have anything in the Mutable signs from 2-6 degrees. During the quoted date range, it may be wiser to hold back rather than pushing ahead. The big adventure may be nothing more than a mirage, or you may be aiming in the wrong direction entirely.
If you're looking for something to ground you, look to Virgo and Scorpio in your chart. Venus in Virgo will be forming an ultra-practical sextile to Saturn (rules) at 19 Scorpio from September 20-21. That's what you can rely on for the truth. Money, love, values (Venus themes) will be your touchstones for reality. Look at the facts. Look at what you actually have, or who has proven their love for you. What you can point to and say "Yes. I know this is it."
Venus in Virgo sextile Saturn is no one's definition of fun, but it will be your anchor.
You'll feel the square if you have anything in the Mutable signs from 2 to 6 degrees. You'll feel the sextile if you have anything in Virgo or Scorpio from 18 to 20 degrees.