病毒堪称牛顿经典机械唯物主义的形象代言人。病毒的感染、扩散、湮灭严格服从drift（铁定趋势），几乎没有diffusion（偶发因素）。预测#债券#的趋势要比预测感染人数难一万倍。你告诉我T_0的感染人数，我用SIR模型就能算出今后任意一天的感染人数，在一定的置信度内绝无差错。

感染人数的发展轨迹接近于Sigmoid函数。Sigmoid的任意一阶导数中依然包含S函数本身，这是其第一大优势。Sigmoid的取值范围为(0, 1)，于是我们可用来表示感染人口的比例（从0%到100%），这是其又一大优势。

下图呈现了感染人数飙升阶段的S函数，当感染人数进入下降通道后，S函数呈现与Y轴对称的相反形状，但right tail相当长，要拖沓很久才渐近于X轴！国内外三本权威的病毒学教材均坚持此观点。

上海6月1日解封后，我一步都没出过小区大门。教练多次约我去拳馆打拳，我都说6月15日以后（最好是建军节以后）我看情况再来吧。

你问我相信谁的话？我谁也不信，我只信病毒，只信SIR模型！

Thanks to all the fans who voted for me. I couldn’t be more proud of winning the Sir Matt Busby Award in my comeback year to Old Trafford and to the Premier League. This award goes to all the supporters who’ve never let us down during a very difficult season. Thank you so much for always being on our side and for helping us get Man. United back on track. We know we can count on you.

Thanks to all the fans who voted for me. I couldn’t be more proud of winning the Sir Matt Busby Award in my comeback year to Old Trafford and to the Premier League. This award goes to all the supporters who’ve never let us down during a very difficult season. Thank you so much for always being on our side and for helping us get Man. United back on track. We know we can count on you.