Yep. There must have been a lot of good signs for them to have lured Alonso and for Button to have put so much effort into staying.
Its such a shame. McLaren spent years being far to cautious, and then when they do decide to take a big risk it bites them in the ass

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They weren't really cautious lately, they built an entirely new car for 2013... which was borderline retarded, but certainly not cautious. Likewise in 2014 they built an entirely new car, and it didn't work, not cautious just inept. They built an entirely new car in 2015 as well.... this isn't new, it's the third year they did something outrageously stupid. A brand new idea every year, doesn't work.. start again.
Throwing everything out the window is almost never a recipe for a great new car. Lewis joined a team that had Brawn, was hiring all the right people(like Ferrari has been doing for the past year), was making good incremental steps and had made early progress on the 2014 engine. There was every sign they were improving. Read up on what Merc guys say, 2013 had speed added to the 2012 design but the base chassis and design had tire wear issues, they fixed that for the 2014 car. Lowe has said the 2013 car was probably a bigger step than 2014 in terms of design of car excluding the engine. The 2015 car is another iteration of the previous car, improve the worst parts of the car, keep the best.
Mclaren.. none of those signs. Early 2015 engine, nooooo, extremely late to the party engine being rushed through design, massive, massive red flag. Incremental successful improvements in the car, or an extremely well respected team boss with loads of previous success... nope. There were loads of signs Merc could come good, almost none at all that Mclaren could. In fact Mclaren were rushing another new chassis, another new philosophy and worst of all rushing the design of a new engine.
Alonso went to Mclaren because he stuck his head out of the Ferrari paddock to see who was interested... while his head was out the Ferrari boss put on a huge pair of brass balls and kicked Alonso all the way out, replacing him. Alonso was stuck with a Ferrari contract, no seat and no one except Mclaren offering a seat.
Alonso is at Mclaren because if he didn't go there he'd be the third driver at Ferrari this year. He didn't see anything, he didn't predict brilliance... it was his only option, plus you know, 20-30 mil a year. I'm sure a lesser team would take him, but they wouldn't offer him 20+ mil a year to drive for them. Of course he has to say he wasn't interested in this or that, so what, his other option is to say he was attempting to get a drive at Merc/RBR because he thought he had a better shot at a title and Ferrari called his bluff and neither RBR nor Merc wanted him.