Are you talking about Blair,
FrankieStein, when you try to tell us what we're feeling and why?
If you are, then I'll say more.
The reason Cameron couldn't go into Syria was the same reason the US limited its involvement: because both countries had entirely spent their credibility and international political capital on the mess that was the invasion and occupation of Iraq.
The US's figleaf of the Iraq invasion being about Al-Qaeda was visibly untrue; the UK figleaf of WMD was quickly shown to have been misrepresented: so the pretence that the invasion was about anything other than US imperialism was seen through.
Then, the US fucked up the occupation in more ways than I have the energy to list here by having no strategy beyond removing Saddam Hussein. I remember all too well things like the US rejection of the Iraqi army (much of which was friendly to the US invasion, initially believing the US rhetoric that it was a liberation), the de-Ba'athification which meant sacking many of the people running civil organisations (because under Saddam people couldn't get promoted in these without token party membership) thus seriously degrading civil society and the rule of law. These and many more things where you don't have to be wise after the event: it was obvious at the time they would create terrible consequences. The US prison camps basically became universities for extremism – they contained talented, experienced men many of whom would initially have been willing to work with the US occupiers but had been given no place to stand and no future. Just as the first post-apartheid government of South Africa was hatched in the university of Robben Island; so the rather different organisation of Daesh was nurtured in US prisons in Iraq.
So by the time of the Syrian civil war, we had no ability to present any intervention as being for the benefit of the invaded country, rather than just another Western imperial adventure. Intervention risked lending credibility to the Islamists' narrative of Islamism being a righteous liberation movement against the imperialist invaders, and acting as a recruiting factor.
Specifically regarding Afghanistan: in the early 2000s, the US & UK diverted resources from the early years of the Afghanistan operation to invade and occupy Iraq; and we did so out of choice, not necessity. The occupation of Afghanistan might always have ended like this – but that lack of resources in the early years made it vastly more likely.
Blair made a highly avoidable mistake by going in with Bush, but the real problem came afterwards because he could never, ever admit that he'd been wrong. So we were trapped in his fantasy world, still acting as though his imaginary universe were true instead of adjusting to the new reality and dealing with it. The UK couldn't change tack on Iraq until Blair departed as PM, and for domestic reasons he was in for so long it was way too late. I can't put my mind on the detailed things I thought at the time the UK could have done to mitigate, because my memory is patchy. But I clearly remember knowing them at the time, and being frustrated that Blair couldn't bring himself even to engage.
If Tony Blair had stuck his head up right now to witter about climate change, I wouldn't much care. On Brexit I think he would actually have done a far better job steering us from the referendum-result to the post-EU future than May and Johnson.
But that's not what he's chuntering about now. He is back gracing us with his opinion on a subject where he was wrong in the first place; then failed to face the fact that he was wrong. I've seen nothing over subsequent years to suggest he's not still in that mental place, and that his further witterings won't be just as rooted in those fantasies and his need to deny his misjudgement.
So excuse me if I don't pay the blindest bit of notice to anything he says.
(NB I'm relying on my memory for much of the above, so am sure there will be details on which I can be corrected.)