It's why Simmons has embarked on his fifth annual Big Walk for dementia research, hoping to raise money to support the 446,500 Australians living with the insidious disease.
Diagnosed with early on-set dementia in his early 60s, the 1991 Penrith premiership winner is dedicating himself to the cause while he still can.
"Everyone's probably different, but I've sort of gone along like I didn't notice too much, but then you have a bit of a dip," Simmons told AAP.
"Then you flatten out and you dip a bit again. I don't think I've got too many more dips left. My memory's getting pretty ordinary."
This year's walk is particularly close to Simmons' heart as he honours late Panthers player and clubman John Farragher, who passed away last year.
A collapsed scrum rendered then-21-year-old Farragher a quadriplegic in only his seventh first-grade game, but he remained involved with the Panthers for almost five decades thereafter.
The Panthers have since built a memorial garden dedicated to Farragher opposite the training field at their centre of excellence.
As his own tribute, Simmons began this year's walk in Farragher's hometown of Gilgandra on Monday.
As his beloved Panthers were holding captain's run for Friday's clash with Canterbury, Simmons spent Thursday trekking from Dubbo - hometown of co-captain Isaah Yeo - to Obley.
Next Friday, having walked 320km, Simmons will finish up in Cowra.
Brad Fittler, James Maloney, John Skandalis and Tony Butterfield are among the rugby league greats joining Simmons for portions of the walk.
For Simmons, the hope is to raise enough money to fund two dementia research programs and to continue supporting families affected by the condition.
"You can't get the message out there enough about awareness," Simmons said.
"No matter how many times you tell people that dementia is the biggest killer of people in Australia, they just don't take it in.
"What's happened lately is it's starting to kill young people and people don't realise that either, they think it's an old people's disease.
"We need to work hard and find an answer."
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