He stayed in the garage for too long. He was delighted with his awesome hiding place; there are a couple moments when he almost decided to bolt and take his chances, but then he heard kids screaming as they were found in succession, so he decided "to hold out a bit longer." He then started daydreaming about how great it was going to be when he emerged victorious, the last one not found. He though about "what fun if they were all found and caught—he alone left unconquered! He had never known that sensation...that would be thrilling beyond imagination." This daydream lead him onto others; time passed, and he still wondered if he heard the kids playing and screaming, and thought he did. But then, with a cold start, he realized that he had forgotten that he needed to touch home base to win. So, "with a whimper he burst through the crack... he flung himself at the white pillar and bawled, 'Den! Den! Den!'" but he was much too late. The kids had stopped playing a very long time ago, and had forgotten him. And then, the tragic end: "The ignominy of being forgotten—how could he face it? He felt his heart go heavy and ache inside him unbearably. He lay down full length on the damp grass, crushing his face into it, no longer crying, silenced by a terrible sense of his insignificance."
So Ravi loses because he stayed too long in his spot, and the other kids moved on, forgetting him, not even acknowledging his feat.
He loses because he had been forgotten and his 'victory' was not valid. After the game started, he opted to hide himself in a garage. Time passed and Raghu has already find everyone, but Ravi was still not found. So he decided to 'hold out a bit longer'. He stayed like that because he wanted to impress and show his friends that he could be the first, as it was the main reason for his staying in the garage. He thought and said that 'he alone would left unconquered'. However, he decided to returned to the house and express his victory thinking that they would congratulate him. Despite, he concluded that he had been forgotten and they this emblematic game that Anita Desai has choosen has already stop being played since a very long time ago. Ravi strained that they sustained the game and continued to play, but unfortunately they refused. The was very unphlegmatic and could not endure that. "this ignominy of being forgotten" was too much for him. So what the use of winning the game but on the other hand your friends dont accept your victory. Ravi temerity drowned him to his conquer and left, as a child he expected lot of jubilation and shrieks of joy and felicity. But instead it was a if the world crumbles on him. For Ravi who depict the essence of innoncence, wining a game and being considered a winner was a majestic thing for him. But in my opinion, it was a bit of Ravi's thought that he lost, he trespass his limit by staying too much hidden, he was too absorb and his mind focus too much on the game. Moreover, Raghu, Mira and his cousins cannot be blaimed for this because it normal to forget someone in playing when you dont find him for too long. But Ravi is still a toddler, he cannot comprehend this!