Bus Rapid Transit starts with a simple idea- why not run buses instead of railcars, and save all that money for rails and signalling? Even better, buses have 'flexibility' that allows them to use city streets and go new places. Best of all, you get to sell the idea of 'rapid transit' but all you have to deliver is buses.
And this will actually work, as long as transit uses decreases and failure is the end goal. But if transit use rises, you're caught short, and have no way to respond to the conditions causing the increase in ridership.
And the BRT mistake can be compounded, as Sound Transit is doing in King County, by building special roads and parking garages for the BRT. Again, in theory, this stuff will be built so it could be used for LRT in the future. In actuality, the east extension of Sound Transit Link service will be a case of building the LRT to fit the BRT infrastructure, not vice versa.
Why is this stuff important? Because of global warming. Well within the lifespans of stuff built today, it will be necessary to build transit to take 40-60% of the market share, not the 5-6% seen today. No transit system in the nation will be able to meet this need with buses, and referring to Curitabo will simply reveal that they eventually built the rail system they needed all along.
The Sound Transit rail route to Bellevue is bent to reach every bus park 'n ride and gather the ridership. Somebody forgot to tell the management that it's not just buses that are 'flexible'- riders can be flexible too. They'll travel further to catch a train then they will to take a bus.