CHICAGO (NewsNation Now) — There’s a toll that comes with being on the run. It can drive a man into madness. The question is: How long might that take for Brian Laundrie? Monday marks exactly four weeks since he went missing.

Joel Lambert, a former Navy SEAL, survival expert and star of the show “Lone Target,” told Ashleigh Banfield that if Laundrie is hiding out in the wilderness, his mental fortitude is probably the most important factor in keeping him alive.

“Your mental mindset is the most important tool and It could also be your worst enemy,” Lambert said.

Lambert joined Banfield to break down what Laundrie might be experiencing each week while on the run. During his first week, Lambert says, there is a rule of threes.

“Rule of threes states that you can survive three hours without shelter, you can survive three days without water, and you can survive three weeks without food,” Lambert said.

In week two, adrenaline can impact the four Fs: fight, flight, freeze and focus.

“With training, an adrenaline response can also be a very positive thing that focuses you against the threat or against whatever it is that you’re dealing with,” Lambert said.

In week three, he’s likely stressed about food.

“If he’s brought food with him, he’s going to be starting to run low and he’s probably been rationing it,” Lambert said. “And so he’s, like I said, (he would experience a) caloric deficit. And that’s going to be affecting all the aspects of his mind and his body.”

In week four, Lambert, discusses fighting one’s own mind.

“If your mindset isn’t …. focused and sharp and conditioned, then your mind is going to cause the cracks that’s going to break everything down,” Lambert said. “Even if he’s innocent, he knows that … he’s being hunted and he can’t go home and he’s on the run. That’s the kind of thing that’s going to weigh very heavy on someone’s mind and it’s going to drag him down and I think that you may see a mental collapse before too long and maybe … like suicide by cop, he might do something very stupid in order to get caught because he just wants to it all to be over.”

It has been weeks since any firm new details emerged in the case.

On Tuesday, the Teton County, Wyoming, coroner will update the public on Gabby Petito’s autopsy.