Something similar happened to me on Beinn Fhada back in April. Reached the plateau to find a whiteout, snow on the ground, no fun. Still, summit fever set in and I pressed on up, occasionally checking my GPS between the massive gusts of wind. As I approached what I believed to be the summit, there was a brief clearing in the whiteout, and I caught a glimpse of the 'true summit' further round the top of the cliffs. With a sigh, I carried on, battling the relentless wind to eventually reach the 'true summit'.
Upon arrival, I was surprised by how small the cairn was. However, mercy! The snow cleared for a few seconds, and I saw the real 'true summit' a few hundred metres further on. I headed down towards it, then had a marvellous idea: why not CHECK THE GPS to see how far the summit truly is - distances can be deceiving in a whiteout.
My reaction was firstly confusion, followed by disbelief, followed by marvel at how STUPID I had been. The 'true summit' I was looking at later transpired to actually be Sgurr a Dubh Doire, at the far Eastern end of the mountain. I had overshot the summit by almost a mile, in a whiteout, without a huge amount of daylight left.
As I'm sure many of you who have had these experiences know, it can be harrowing. The bottom line is, as Sloosh rightly pointed out:
sloosh wrote:you can have as many maps, compasses, GPS units, mobile phones, whistles, torches or whatever else you like but they're only any use to you if you actually use the darn things!
NB - and if in doubt about the weather, TURN BACK