Why? Well, because some of its positive charge will be dissipated to this electron. So that means our final effective nuclear charge will be less. So the way we find our effective nuclear charge is using the following formula. Our effective nuclear charge given by ZF equals to the nuclear charge or the actual nuclear charge of our proton nucleus minus the average number of electrons separating our outermost electron and our proton nucleus. And we see that for helium, if our nuclear charge on our proton nucleus is two, then this guy actually feels a charge of 1.69, because we're subtracting the charge that this guy experiences.