Why a few months is the realistic comfortable pace
The sorting and sentimental-decision phase is usually the slowest part, not the physical move itself — deciding what to keep, offering pieces to family, and giving people time to actually claim things takes real calendar time if it's going to be done without rushing anyone into a decision they'll regret.
Selling higher-value furniture or belongings also takes time — a marketplace listing or consignment arrangement can sit for weeks before it sells, so starting that process early is what actually determines whether it succeeds before a moving deadline, not how motivated the seller is.
What compresses the timeline, and what it costs
A health event, a sudden move, or a house sale that's happening faster than expected can compress downsizing into weeks instead of months. The main trade-off is that selling higher-value items becomes impractical on that timeline, so more goes to donation or, in some cases, is simply left for a cleanout service to handle as part of an as-is house sale.
That's not a failure — it's a legitimate choice when the actual priority is getting the move or sale done, not maximizing the value recovered from every individual item.
Starting the house sale and the downsizing sort at the same time
If the plan includes selling the house itself, there's no requirement to fully finish downsizing before that process starts — a listing or a cash offer conversation can begin in parallel with sorting, especially with an as-is buyer who doesn't need the house staged or fully cleared to make an offer.